Sorry, but this is not a debug level 10 log of winbind.
Please set
debug level = 10
debug pid = true
max log size = 0
in your smb.conf, restart winbind, reproduce the problem and send all the Samba-related logfiles. Then remove those lines from the smb.conf again and restart winbind again.
Thanks,
Volker

After Upgrading from FreeNAS 9.2.1.5 to 9.2.1.6 RC we also find this error every five minutes in our logs.
We use FreeNAS as Backup-to-Disk media for Backup Exec 2014. This Backup-to-Disk folder is configured as UNC path in Backup Exec. After reading this message https://bugs.freenas.org/issues/5054#note-18 I simply disabled the Backup Exec services for testing purposes for 15 minutes and the error messages are gone. So it looks like to me, that this error is coming from programs, services etc., which are accessing the CIFS share via UNC path.
I will upload the logs as .zip file